Lasers have been controlled with diverse electronic circuits. It is desired to provide a laser control employing an array of digital-to-analog convertors in which calibration of such array is facilitated. Such laser controls find usage in diverse laser applications. One such application is in optical disks.
It is a continuing desire to increase areal density of optical disk recording. One way to increase area density is to increase linear recording density along tracks on the optical disk. Earlier optical disk employ pulse-position modulation (PPM) wherein a pulse in a predefined position along a track indicates a binary one and absence of a pulse at that position indicates a binary zero. It should be borne in mind that rather than representing user data values, such indications indicate 1's and 0's of a recording code, such as the well-known d,k codes. Intersymbol interference (ISI) in PPM recording tends to limit the linear recording density of optical disks. Pulse-width modulation (PWM) can increase linear recording density over PPM recording techniques. PWM introduces a need for an enhanced recording system. One such enhanced PWM recording system is shown in Belser et al U.S. Pat. No. 5,400,313. In the Belser et al patent, a minimal number of circular marks are recorded on the optical disk to record a desired run length code pattern. A preferred coding is a known d,k code having 1,7 parameters. The Belser et al recording system provides for accurately locating pulse signal transitions on the optical disk, a necessity for high-density PWM recording. A plurality of laser recording power levels are used. One level drives the laser for reading. A second level drives the laser for idling. Additional multiple power levels drive the laser for writing data to the optical disk. The multiple power levels for writing are added to the idling or base laser power level. Such base power level is termed a "threshold current" or CUT power level. The threshold is that power level below which the laser does not emit a laser beam. That is, it is the smallest laser drive current level at which the laser emits a coherent beam of radiation. These power levels are determined using recording patterns for accurately obtaining readily detectable recorded PWM signal transitions.
It is also desired to minimize elapsed time between mounting an optical disk and a first access to that mounted optical disk. Since determination of optical device and optical medium conditions that affect laser operations are time consuming, it is desired to reduce calibration time to a minimum without sacrificing an optimal laser writing (recording) and reading operations.
Optical disks have a format of addressable sectors disposed in a spiral track. An optical data disk is rotated relative to a laser beam at a constant angular speed for scaling a laser beam along the spiral track. In contrast, optical video/audio disks are relatively rotated at variable rotational speeds to obtain a constant linear laser beam scanning speed. In any event, while scanning a laser beam along a relatively moving spiral track, automatic track following techniques keep the beam on the spiral track. This arrangement applies to both rewriteable and write-once optical disks. In optical data disks it is usual in each sector to have an address portion, herein termed identification (ID) portion, and a data-recording portion. Any type or format of data may be stored in such data-recording portion. In rewriteable optical disks, such as magneto-optical and phase-change disk, a write power qualification or test field may be disposed between the ID portion and the data-storing portion. This field is termed Automatic Laser Power Correction (ALPC) in which write pulses are recorded to qualify a laser write power level before recording. Qualifications of the laser write power (sufficient power to reliably record in the data-storing area but not excessive power) is termed Automatic Laser Power Qualification (ALPQ). It is to be understood that many known details other than set forth herein are used in writing data to and reading data from optical disks.